This invention relates to a pumping system adapted to raise a liquid, more particularly water, from an underground level to a utilization level, said system being actuated by the thermal flux radiated by the sun, through the agency of a vaporizable fluid.
In those parts of the world which have long periods of sunshine, the use of the thermal flux radiated by the sun to produce energy has been the subject of numerous tests and some applications. The relatively low radiated power density, on average of the order of 1 kilowatt per square meter during periods of sunshine, and the low thermodynamic efficiency obtainable in relatively uncomplicated installations, mean that this energy production is rarely competitive with conventional energy production processes.
Nevertheless, in underdeveloped areas far from conventional energy production centers the cost of transmitting such energy may offset the low efficiency of solar installations and make the latter competitive.
Applications are known in which solar energy is used for pumping water from underground levels. Such applications generally use a vaporizable fluid which is heated and vaporized in solar panel evaporators, the vapor produced being fed to a motor which actuates a pump adapted to draw water from the underground level and raise it to a utilization level, for example a water-tower.
A solar panel evaporator comprises a surface aimed on average at the sun and blackened for optimum absorption of the solar flux, and a tube or nest through which a fluid for vaporization passes and in thermal contact with the absorbent surface; the solar panel is generally thermally insulated to avoid heat losses to the atmosphere, and its surface exposed to the sun is covered with glazing to protect it from dust and reduce thermal losses due to convection, or the glass-house effect.
The motor is generally a reciprocating piston engine which is better than a turbine for withstanding the pressure and vapor flux variations due to the daily and seasonal variations in the solar flux picked up by the evaporator panels; also, the operating characteristics of the piston engine are better suited to the operating characteristics of the pump.
Since the temperature of the hot source formed by the solar panels is less than the boiling point of water, at least in marginal sunshine conditions, water cannot be used as vaporizable fluid; a fluid having a lower boiling point must therefore be used so that the pressure in the evaporator at mean operating temperature is at a few bars. Free discharge is impossible in that case and the vaporizable fluid must flow in a closed circuit, with a condenser and a circulator to feed the vaporizer with condensed fluid under pressure. The presence of a condenser also improves the thermodynamic efficiency of the installation.
Such installations exist and operate correctly but they have a number of drawbacks.
The piston engine must be disposed above ground for maintenance and supervision; the pump it drives may be situated at the same level for direct coupling to the motor if the water to be pumped is not at too deep a level, i.e., less than 8 to 9 meters lower than the pump, since otherwise the pump must be lowered towards the underground water and coupling to the motor becomes complicated and a source of energy losses due to mechanical friction.
The motor cannot start itself under the effect of pressure following progressive heating of the vaporizer in the morning, for example; an adequate pressure has to build up in the vaporizer to ensure an operating speed and vapor flow equivalent to smooth operation.
The condenser must be immersed in a cold source; if it comprises a radiator with natural cooling, the radiator must be very large and protected from the solar radiation; ventilation of the radiator by forced air flow consumes energy.
The piston and piston rod packings cannot be perfectly sealing-tight in practice and vaporizable fluid has to be replenished from time to time.
Finally, operation and mechanical maintenance of the installation necessitate the presence of a skilled supervisor, and this restricts the location of such installations to relatively large centers.